Implemented basic timezone handling. Default zones can be set as context (EWSClient#set_time_zone) or override for start and end times. Implemented #get_time_zones to request all available time zones.
Doc fixes.
Merge branch 'feature-time-zone' into merged-features

Conflicts:
	lib/ews/ews_client.rb
	lib/ews/soap/builders/ews_builder.rb
	lib/ews/soap/exchange_web_service.rb
	spec/unit/soap/builders/ews_builder_spec.rb
Merge branch 'fixes' into merged-features